[a11y] Add histogram for Reduced Animations setting.

BUG=b:260208248
TEST=None
AX-Relnotes: n/a.

Change-Id: Ib64f50361378d07bea405de049548d7776c0d161
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5408591


Reviewed-by: Evan Liu <evliu@google.com>
Reviewed-by: Akihiro Ota <akihiroota@chromium.org>
Commit-Queue: Tzarial Kuznia <zork@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1282779}